Several TiO2-carbon nanotube composites were prepared by ball milling procedure. Prepared materials were characterized by several techniques, including N2 equilibrium adsorption isotherms, thermogravimetric analysis, elemental analysis, X-ray diffraction spectra and transmission emission microscopy, and tested in the mineralization of oxamic acid (OMA) by photocatalytic ozonation. The influence of milling conditions was evaluated and the performance was compared with samples synthesized by conventional procedures. Independently of the milling time, a high amount of OMA, approximately 70%, is removed in the first 10min of reaction by composites of commercial TiO2 (P25) and carbon nanotubes (MWCNT). In the best conditions, the milled sample presents a reaction rate constant of 0.099min−1, in contrast to 0.082min−1 obtained with conventional composite. The presence of N-groups produces a negative effect, especially when N-precursor was added during P25 composite preparation, removing 30% of OMA after 10min of reaction and decreasing the removal rate to ≈0.050min−1.The OMA degradation is significantly more efficient in the presence of the milled composites containing synthesized TiO2 (SG) when compared to the composite prepared by the conventional procedure increased OMA removal from 40% to 70% after 30min of reaction. The reaction rate constant of milled sample with original MWCNT (0.032min−1) is considerably higher than observed with unmilled (0.012min−1). A remarkable conversion is observed for all SG milled composites during the first 30 min of reaction and the presence of Fe is advantageous, since Fe can promote the O3 decomposition into HO radicals and surface reactions.